In an electric machine, the main parts are the rotating rotor and the static stator around the rotor. A key part of the rotor and stator is the core or core package which stator core is composed of stacked and fixed laminated sheets. The highly stressed core is prone to wear which leads to instability over the years of operation. A regular maintenance of the core is necessary thus to assure the stability of the core. The pressure in a stator core is of paramount importance for long and safe machine operations, loose cores generate vibrations leading to stator failures. Several methods and devices are proposed in the state of the art. One method is to arrange a blade or wedge which carries an instrumented tip between the sheets of the core. This method is used to measure the pressure between the core laminations. The reliability of this test method is however in question and only allows the assessment of largely slack cores with highly impaired tightness.